The dietary supplements market is big business. In 2021, it was estimated to be worth around $149.5 billion, and this figure is projected to rise to around $240 billion by 2028. It seems that billions of us are now popping pills every day, in the hope that they will improve our health. With the stakes this high, no wonder that manufacturers of vitamin pills are keen that we keep taking the tablets.
However, does the evidence for the value of these supplements live up to the hype? Or is taking supplements while continuing to eat largely unhealthy diets a case of trying to ‘have our cake and eat it’? This page examines that question, and provides the evidence on the use of supplements.
What are Supplements?
What do we mean when we talk about dietary supplements? The box below shows that this is far from simple.
Definitions of food and dietary supplements
“A dietary supplement is a product intended for ingestion that, among other requirements, contains a “dietary ingredient” intended to supplement the diet. The term “dietary ingredient” includes vitamins and minerals; herbs and other botanicals; amino acids; “dietary substances” that are part of the food supply, such as enzymes and live microbials (commonly referred to as “probiotics”); and concentrates, metabolites, constituents, extracts, or combinations of any dietary ingredient from the preceding categories.”
The US Food and Drug Administration
“A food supplement is...any food the purpose of which is to supplement the normal diet and which is a concentrated source of a vitamin or mineral or other substance with a nutritional or physiological effect, alone or in combination and is sold in dose form.”
UK Food Standards Agency
Why Take Supplements?
Fundamentally, dietary supplements are intended to add something to the diet that would otherwise be missing, or to top up the supply of a particular substance.
The most common—or perhaps best known—supplements are probably vitamins and minerals, especially vitamin D and iron, and fish oils. These are often recommended to people who feel a bit tired or run-down, in the hope that they will solve the problem. However, many people routinely take supplements every day.
Protein supplements are also common, often in the form of powders that can be reconstituted with water to make protein drinks. These are most likely to be used by bodybuilders, although sometimes they are used as part of a weight loss diet.
There are also many hidden supplements added to various foods, including bread, breakfast cereals and other ultra-processed food. These include vitamins, minerals and folic acid. These supplements were first added to foods routinely back in the early to mid-twentieth century, as a way to avoid malnutrition in poorer populations. Indeed, the addition of folate to bread was very much a success story in reducing the number of children born with spina bifida.
However, the quality of diets has now improved significantly.
A shortage of nutrients is unlikely to be a problem for anyone consuming a healthy balanced diet containing plenty of fresh fruit and vegetables. Indeed, the main problem in developed countries now is a combination of ‘over-nutrition’—eating too much—coupled with a reliance on ultra-processed food such as those very items containing the supplements.
Why, then, do we continue to take them?
The answer is because we have been told that they are good for us—usually by the same supplements industry that has so much to gain by keeping us convinced. Perhaps more cynically, maybe we also like the idea that we can just take a pill and our health will magically improve without any other changes to our lives or diets.
The Evidence About Supplements
Overwhelmingly, however, the evidence is that supplements not only don’t improve our health—but they could actually be harmful.
First, it is worth looking at the regulation of dietary supplements—or rather, the lack of it.
There is very little regulation of dietary supplements. In the US, dietary supplements are covered by the Food and Drugs Administration (FDA). However, the FDA cannot challenge data from companies selling supplements without doing its own research first. Realistically, this means that safety and efficacy of supplements is never checked. Indeed, the content of supplements is unlikely to be checked, even though some unexpected ingredients have been found in some products (see box).
Unexpected item in bagging area?
It is wise to be wary about what you are buying. Crushed Viagra and anabolic steroids have both been found in some ‘multivitamin tonics’.
Other countries may regulate supplements slightly more than the US, but it is still difficult to know exactly what you are buying.
What’s more, there is very little evidence that supplements achieve anything.
Even vitamin D, possibly the most studied and prescribed vitamin of all, does not live up to the hype (see box).
Case study: Vitamin D
Over many years, studies have shown a clear association between low levels of vitamin D and various problems, including autoimmune diseases, heart disease, depression and cancer. Many doctors have jumped on this association, and prescribed supplements to help with these conditions.
The problem is that the association is not causal.
The deficiency does not cause the disease. It is more likely that the disease causes the deficiency.
What about vitamin D and bone density? Surely that’s proven?
No. A recent high quality clinical trial on the use of vitamin D and calcium to prevent fractures found absolutely NO evidence that either vitamin D or milk (for calcium) had any effect on the incidence of fractures.
High quality studies have also found that taking omega-3 fish oils in supplement form does not decrease the risk of heart disease or cancer. In fact, it has absolutely no effect on your chances of dying from any cause.
In other words, supplements don’t do any good. But can they cause harm? The evidence shows that they certainly can.
Good studies of more than half a million people taking multivitamins have found that they were more likely to develop cancer or heart disease. Taking supplements of vitamin E and selenium has been linked to higher levels of prostate cancer.
More routinely, there are now so many products that are supplemented with vitamin D, iron and folate that overdosing is becoming a very real possibility. Vitamin D, like vitamins A, E and K, is fat-soluble, and therefore stored in the body. It can affect the brain, kidneys and heart. Indeed, its overuse has been linked to reduced bone density and increased fractures—the very problem that taking it was designed to solve.
“The supplements really don’t work”
Chapter heading, Spoon-Fed: Why Almost Everything We’ve Been Told About Food is Wrong by Tim Spector
The Problem with Supplements—and the Solution
The problem is that when we take a supplement, we are effectively dosing ourselves with a chemical.
It is very different from eating a substance within a food, along with other foods. Our bodies have evolved to process food—but not necessarily high doses of particular chemicals often found within foods.
Instead of taking supplements, the evidence suggests that we should all be eating a more natural, balanced diet. In particular, we should be eating plenty of a wide variety of fresh fruit and vegetables, and avoiding high-sugar, ultra-processed food. We should also try to get at least a few minutes of sunshine every day. For most people, this will provide all the vitamins and minerals that you need.